Why Zeiss exposes 1 stop brighter than Nikkor

<p>I ran a comparison test for Zeiss 25mm/2.8 CPU ZF.2 lens vs. Nikkor 17-35/2.8. Shot the same subject with a tripod and no filters on lenses on D3. What struck me is that Nikkor image came out lighter and less contrast than the Zeiss image.<br>

When I checked the exposure here is what I got:<br>

Zeiss - f2.8, 1/320, ISO 200<br>

Nikkor (on 25mm) - f2.8, 1/160, ISO 200<br>

When I corrected Nikkor by -1 in Photoshop the images' histograms became very much alike. The same 1 stop difference was happening on other apertures as well.<br>

Does anyone have an idea where this difference is coming from?<br>

Thank you</p>

 

<p>You moved you cam a little when you changed lenses, maybe?</p>

<p>How come you aren't testing this in manual, controlling it so that you have the exact same shutter speed and aperture? <br>

Of couse the Nikkor will be brighter, you have a slower shutter speed than you used with the Zeiss...</p>

<p>Are you possibly asking why the CAMERA metered differently with a different lens attached? Metering systems are unreliable. That's about all I can say on that topic.</p>

<p>There is no difference, the two lenses work the same. The pictures taken at 1/160 are obviously 1 stop brighter than the pictures taken at 1/320. That's all</p>

<p>Did you cover the viewfinder eyepiece when you took the pictures?</p>

<p>I believe the OP means that his camera is metering differently.</p>

<p>Difference between f/stop (measured numerically based on mathematical calculations of physical properties) and t/stop (measured by actual light transmission, which is based on more factors than just f/stop).</p>

<p>It is not unusual for two lenses with an 2.8 f/stop to have different t/stops (perhaps on is 2.9 and one is 3.3).</p>

<p>I bet it's that simple. Nothing wrong here.</p>

<p>Check the lenses under "sunny 16" conditions and you'll quickly find out which lens/lenses are giving your wrong exposure. Potentially both are wrong.</p>

<p>A single-focal length lens (i.e., prime) is not exactly the same as a multi-element zoom lens.</p>

<p>Is there a reason you expect both lenses to be exactly the same? Light travels through a lens to the camera meter, you set the exposure, and the image is recorded on the sensor. You did not state under what lighting conditions (i.e., sunshine, indoors with ceiling lights?) for your test, so each lens has different characteristics.</p>

<p> </p>

<p>Thanks to everyone for all the suggestions.<br>

I took several shots at apertures 2.8, 4.0 and 11.0. The same x2 difference in shutter speed was observed. Matrix metering was used. And I used a tripod - some movement was possible, probably, less than 1mm. The subject was outdoors a shady corner with some sunlight and all shots were taken within 2 minutes. Lighting conditions did not change dramatically (they surely changed to some minor extent).<br>

I have to run some more experiments with other lenses to see which causes this difference. And please note that when I shifted exposure on Nikkor image by -1 the pictures histograms started looking very much the same.<br>

I did not expect the lenses to be :the same" and expected differences in rendering but did not expect that big difference in metering.</p>

<p>Mikhail the light metering by your camera is different.<br>

If you expose with the two lenses at same aperture but different time the result must be different. And this is what you get. It is that simple.</p>

<p>The obvious problem here is that the camera decides that different exposures are needed. We all do not know what matrix metering does exactly but what we know is that matrix metering "figures" out what might be the best exposure for a given situation. Even slight changes can influence this "thinking" process. Your camera decides that different exposures are needed for the two different lenses even though you think it should not.<br>

Matrix metering is not a simple process like using a hand held light meter. Some sort of "artificial intelligence" is involved. Sometimes it may be too much "intelligence" :-P</p>

<p>To compare if the lenses act differently try an exposure with a fixed aperture and fixed exposure time (set this in manual mode and keep ISO constant).<br>

Any difference that shows up will be due to differences between the lenses.</p>

<p>PS: Are you certain that matrix metering was used for shooting with both lenses? Is the Zeiss lens chipped?</p>

<p>Try this.</p>

<p>Wide open... shoot a blank white wall with the brighter lens at a manual exposure at such an exposure that the white is not blown out (i. e. so it's some medium gray).</p>

<p>Now, shoot the other one, manual exposure, SAME wall, same f/stop same shutter speed.</p>

<p>Now do the same thing stopped down, say, two stops.</p>

<p>Compare.</p>

<p>Perhaps they look the same or similar wide open (again, ACTUAL light transmission plays in here), but very different stopped down.</p>

<p>In that case, it's possible that one of the lenses has an aperture that is inaccurate when stopped down. Fixable? probably</p>

<p>The camera meters with the lens wide open. Since you're using matrix metering, the camera will be considering the edges of the frame, and not just the center. So to make this comparison with automatic metering, you should be sure that the lenses are set to the same focal length and that the stuff in the frame is all the same (and lit the same way). You probably already thought of that.</p>

<p>You might also be seeing the effects of differences in the vignetting (light falloff in the corners) of the lenses when they're wide open. If the Nikkor zoom has more falloff, the matrix metering might want to give it more exposure.</p>

<p>You should be able to set the D3 so that it lets you control the aperture with the aperture ring, which will ensure that the lens will mechanically limit the amount the aperture closes, instead of electronically reporting it the the camera as the camera closes the aperture. Doing this might suggest whether there's a lens CPU problem. But if you're seeing this metering difference even when you set the exposure to use f/2.8 (and not stopped down some), that's probably not an issue.</p>

<p>My guess is that the issue is different transmission and vignetting values for the two lenses.</p>

 

<p>Thanks to all for the comments and suggestions. I was not prepared for this difference in metering results, hence, the confusion. :)<br>

I may say that this difference is observed consistently irrespective of the subject (I tried two different scenes), time of day (tried for two days in the row and slightly different time), length of the experiment (2 minutes for the entire set), aperture (stopped down to f11). Focal lengths were set equal. Zeiss lens is a CPU lens.<br>

I may try the same in a totally controlled environment, like, shooting a wall or something similar.<br>

On the side note, thinking that I have a flawed Nikkor [not coming that route to Zeiss yet :) ] I also compared this morning the Nikkor 17-35/2.8 with a Nikkor 35/2.8 at 35mm. There was a minor difference of 1/3 of a stop, but nothing that dramatic.<br>

Time to read books on exposure metering theory. :) Thanks to everyone for stimulating submissions.</p>

<p>Generally Nikon cameras recognize their own (CPU) lenses and know how much vignetting etc. it has wide open. Also the peripheral spot meters are corrected for differences in the optical paths. With manual focus lenses, even chipped ones if they're not Nikon P or D lenses, this corrective data generally doesn't exist so you may get some differences in exposures if you trust the meter. The central spot meter should still work correctly though (at least with the standard screen).</p>

<p>It is my understanding that TTL metering is sensitive to the position of the exit pupil of the lens. Lenses from the camera manufacturer are designed to give proper results for the TTL meter but other lenses may not. When I use a Mamiya shift lens on my Canon 5DII the camera is generally off the correct metering by several f-stops except in certain off-center shift positions when the light apparently collimates correctly on the light meter in the camera. I would assume, however, that Zeiss lenses specifically designed for Nikon cameras meter correctly. So maybe I'm wrong or the Zeiss Ingenieure goofed up.</p>

<p>Just to re-iterate, the guy who said T-stops make the difference is probably correct. F/5.6 is the same number on every lens, but that does NOT mean every lens transmits the same amount of light at f/5.6. I have a Schneider 16mm Cine lens which is marked in both f/stops and T/stops on the barrel. T/stops are in green so you KNOW which system is tested as more accurate. This was and probably still is very common on professional motion picture lenses. Very few still photo lenses are marked in T/stops because it's assumed amateurs don't need that much precision.</p>

<p>A zoom lens has more elements and will transmit less light than a prime lens. This is normal.</p>

<p>You may be using the wrong settings with the Distagon ZF.2 lens, or have a deffective or mis-calibrated D chip.</p>

<p>To make an accurate comparision, each lens must see the same target and use the same settings in the TTL meter. Use a gray card which fills the viewfinder and is illuminated uniformly. Try setting the Distagon with the command wheel (if possible) and the diaphram dial. Make sure the camera is using the same f/stop as set on lens. Make sure both lenses use matrix (or center-weighted) metering. Compare with hand-held meter reading. You might not get perfect agreement, but ideally within 1/2 stop or less.</p>

<p>I get the same readings with my 12 element 17-35/2.8 as with a 55/2.8 AIS having only 5 elements or 16 element 70-200/2.8 VR. My light meter (Sekonic L-508) works the same with Nikkor zoom lenses and my Hasselblad (Zeiss) lenses, which include three Distagons (40, 50 and 60).</p>

<p>Thanks to all folks - all these contributions are very informative. I will run more controlled experiments tomorrow and let you know what the results would be.</p>

<p>For one thing, you are somewhat comparing apples and oranges. You are comparing a zoom and a prime. As a general rule, even today with better zoom lenses, primes will usually beat zooms in contrast. Also, you are talking about two different brands of lenses. It is not unusual for the camera to meter a little differently with two different lenses. And remember f-number and t-(transmittance) number are not the same thing. The more elements, the less light will reach the film. It is improved with good coatings, but it is still a physical fact of life.</p>

 

<p>Scott,<br>

I understand that prime is better than zoom, and probably Zeiss prime may be better than Nikon. As a matter of fact this prime beat Nikkor in contrast, color rendering and resolution on the borders wide open.<br>

I also understand that metering might be <em>somewhat </em>different. Still difference of 1 stop struck me as surprising and I wanted to understand the root cause of that.<br>

Thanks for input.</p>

It is absolutely t stops as stated before. I don’t see why people are just assuming the lenses are bad. Op keeps ignoring the t stop posts. It’s simple as that. This is not out of the ordinary. F stops are approximate, t stops are absolute.

It is absolutely t stops as stated before. I don’t see why people are just assuming the lenses are bad. Op keeps ignoring the t stop posts. It’s simple as that. This is not out of the ordinary. F stops are approximate, t stops are absolute.

What is it with answering on 10 year old posts lately?